Genome coding phytolacca antiviral protein and a recombinant expression vector therefor

ABSTRACT

The present inventors discovered a novel genome coding Phytolacca insularis antiviral protein(PIP) isolated from Phytolacca insularis Nakai; and developed a recombinant vector for said PIP genome expression and a microorganism transformed therewith. PIP genome of the present invention has nucleotide homology of about 82%, compared with the genome of Phytolacca americana antiviral protein isolated from Phytolacca americana L., which is closely related to the Phytolacca insularis Nakai. PIP cDNA is consist of 918 bp of one open reading frame and termination codon; and polyadenylation signal which is ubiquitous in mRNA of most plants and animals, appears to be located in the upstream of 33 bp from the polyadenylation site. Recombinant PIP of the invention was proved to inhibit the growth of E. coli HB101 transformed with said expression vector.

This is a continuation of application Ser. No. 08/210,396, filed Mar. 17, 1994, now abandoned which is a division of application Ser. No. 08/138,636, filed Oct. 15, 1993 now U.S. Pat. No. 5,348,865.

FIELD OF THE INVENTION

The present invention relates to a novel nucleotide sequence and a recombinant vector, more specifically, a novel genome coding Phytolacca insularis antiviral protein ("PIP") isolated from Phytolacca insularis Nakai and a recombinant expression vector therefor.

BACKGROUND OF THE INVENTION

Studies on the antiviral proteins from many different plant species, have been carried out, starting from the discovery of pokeweed antiviral protein ("PAP") isolated from crude extract of Phytolacca americana L. see: Irvin, J. D., Arch. Biochem. Biophys., 169:522-528(1975)!. In addition to the PAP, antiviral proteins have been isolated from several plants, e.g., Rich(from Ricinus communis) see: Halling, K. C. et al., Nucleic Acid Res., 13:8019-8033(1985)!, Mirabilis antiviral protein("MA P", from Mirabilis jalapa L.) see: Kataoka, J. et al., J. Biol. Chem., 266:8426-8430(1991)! and α-trichosanthin(from Trichosanthes kirilowii) see: Zhang, X. et al., Nature, 321:477-478(1986)!. Said antiviral proteins have been reported to be ribosome inactivating proteins("RIPs") having RNA N-glycosidase activities see: Endo, Y. et al., J. Biol. Chem., 263:8735-8739(1988)!.

In general, PAP from Phytolacca americana L. is classified as PAP-I, PAP-II and PAP-S that appear in spring leaves, summer leaves and seeds, respectively; and it is known that antiserum reactions among these PAPs are different see: Irvin, J. D. et al., Arch. Biochem. Biophys., 200:418-425(1980)!. Further, it has been known that ribosome of Phytolacca americana L. is depurinated by RNA N-glycosidase activity of PAP. On the other hand, immunoconjugate of PAP with CD4 or CD19 has been reported to inhibit the replication of human immunodificiency virus type 1 see: Jansen, B. et al., Cancer Res., 52:406-412(1992); Kim Y. W. et al., J. Immunol., 144:1257-1262(1990); Myers, D. E. et al., J. Immunol. Methods, 136:221-238(1991)!; in this connection, said PAPs have been supposed to be applicable to the treatment of AIDS. Accordingly, studies on the PAPs in a view of molecular biology have been actively carried out, including the nucleotide sequence analysis of cDNA and structural gene of PAP; precise celluar mechanism of PAP's biological activity; preparation of transgenic plant; and, application of the immunoconjugate.

Under the circumstances, the inventors have made an effort to isolate antiviral protein from Phytolacca insularis Nakai originated in Ulung-Do in Korea, which is closely related to Phytolacca americana L. in terms of phylogeny.

SUMMARY OF THE INVENTION

In accordance with the present invention, a novel antiviral protein (PIP) from Phytolacca insularis Nakai has been discovered; and, the inventors also discovered the nucleotide sequence of genome coding PIP is novel.

Further, the inventors developed a recombinant vector for said PIP genome expression and a microorganism transformed therewith.

A primary object of the present invention is, therefore, to provide a novel nucleotide sequence of PIP genome.

Another objects of the present invention are to provide a novel recombinant vector for PIP expression and a microorganism transformed therewith.

BRIEF DESCRIPTION OF DRAWINGS

The above and the other objects and features of the present invention will become apparent from following descriptions given in conjunction with the accompanying drawings, in which:

FIG. 1 is a photograph showing agarose gel electrophoresis pattern of pJMC511 containing PIP genome;

FIGS. 2A and 2B illustrate a full nucleotide sequence of PIP genome isolated from cDNA of Phytolacca insularis Nakai and amino acid sequence translated therefrom;

FIG. 3 is a comparative diagram illustrating the amino acid sequence homology of the active sites of PIP and the other ribosome inactivating proteins(RIPs);

FIG. 4 is a scheme depicting stepwise construction strategy for expression vector pMS12 of the invention;

FIG. 5 is a photograph showing agarose gel electrophoresis pattern of expression vector pMS12;

FIG. 6 is a graph showing growth pattern of HB101 harboring pMS12;

FIG. 7 is a photograph showing SDS-PAGE pattern of proteins

purified from E. coli HB101 harboring pMS12; and,

FIG. 8 is a photograph showing SDS-PAGE pattern of in vitro translation of purified PIP.

DETAILED DESCRIPTION OF THE INVENTION

To isolate a genome coding PIP, mRNA is purified from leaves of Phytolacca insularis Nakai and cDNA library construction thereof is followed; and, PIP genome is isolated by employing PAP genome. Deletion mutant is prepared using Erase-a-Base system(Promega, U.S.A.); and full DNA nucleotide sequence of PIP is determined by Sanger's dideoxy chain termination method see: Sanger, F., Science, 214:1205-1210(1981)!.

For the expression of isolated PIP gene, commercially available FLAG™ vector(International Biotechnologies Inc., U.S.A.) is employed. Since isolated PIP genome has signal peptide, coding region is synthesized using N-terminal primer and C-terminal primer. Amplified DNA is electroeluted, digested with HindIII, ligated into FLAG™ and expression vector pMS12 is prepared. Said pMS12 is deposited with the Korean Collection of Culture and Microorganism(KCCM), an international depository authority(IDA) on Aug. 28, 1993 as deposition No. KCCM 10040.

pMS12 thus prepared is transformed into competent E. coli HB101 strain treated with CaCl₂ and colonies harboring pMS12 are selected. PIP is induced by culturing said strain on LB broth media containing IPTG(isopropyl-β-D-thiogalactoside) and ampicillin for 6 hrs. After PIP induction, cells thus cultured are harvested, washed with phosphate buffered saline(PBS: 0.01M NaH₂ PO₄, 0.15M NACl, pH 7.4) solution two times; and lysis of cell pellet is carried out by freezing in dry ice-methanol bath and thawing at 37° C. Centrifugation is followed and supernatant thereof are collected. For the purification of recombinant PIP, said supernatant is loaded on anti-FLAG M1 affinity column and eluted with the PBS solution containing 1.0 mM CaCl₂. Synthesis of PIP is determined by SDS-PAGE after synthesis of protein employing in vitro translation technology.

The present invention is further illustrated in the following examples, which should not be taken to limit the scope of the invention.

EXAMPLE 1

Isolation and nucleotide sequence determination of PIP genome

10 g of the leaves of Phytolacca insularis Nakai was homogenated using liquid nitrogen. To the homogenate thus prepared was added buffer solution(0.18M Tris, 0.09M LiCl, 4.5 mM EDTA, 1% SDS) for RNA isolation; and centrifugation at 10,000 rpm for 20 min was followed. To eliminate protein and impurities from supernatant, phenol/chloroform extraction and chloroform extraction were carried out in a serial manner; and total RNA was isolated from the supernatant after LiCI sedimentation. mRNA was isolated from total RNA using oligo(dT) cellulose column chromatography, and 5 μg of mRNA thus isolated was used for cDNA synthesis employing ZAP-cDNA synthesis kit(Stratagene, U.K.). Synthesized cDNA was linked to EcoRI adapter, and fractionated by Sephacryl S-400 spun column in accordance with molecular size of cDNA. cDNA thus fractionated was ligated to Uni-Zap XR vector(Stratagene, U.K.), and in vitro packaging employing packaging extract was followed.

To isolate PIP genome from the cDNA library prepared, PAP genome was isolated from cDNA library of Phytolacca americana L. and, 0.5 kb EcoRI fragment of said PAP genome was labelled with DIG-Labeling & Detection kit(Boehringer Mannheim, Germany); and, product thus obtained was employed as a probe for PIP gene isolation. E. coli XL1-Blue was infected with phage on petri dish to form plaque of 2×10⁴ pfu and incubated at 37° C. for 12 hrs. 5 clones were obtained from the 1st screening procedure and 2nd screening was followed in a similar fashion as above, with the exception of changing plaque number of 5×10² pfu. To transfer phagemids of 4 recombinant Uni-Zap XR phages obtained from the 2nd screening, in vivo excision technique employing R408 helper phage was carried out. Plasmids were isolated by alkali lysis method from the B colonies thus selected, and colonies harboring PIP genome were screened by double restriction with EcoRI and XhoI.

To determine nucleotide sequence of PIP genome, the clone 5 was selected from the isolated colonies, and subcloned on pBlueScript SK(-) vector. The clone 5 DNA was double restricted with EcoRI and XhoI, subjected to self ligation, and transformed into competent XL1-Blue. The clones cultured on LB media(10 g/l Bactotrypton, 5 g/l Yeast extract, 5 g/l NaCl, pH 7.5) containing 50 μg ampicillin, were selected and plasmids were isolated by alkali lysis method, and colonies harboring 0.7 kb and 0.5 kb EcoRI/XhoI fragment were selected.

FIG. 1 shows an electrophoresis pattern of pJMC511 harboring PIP genome(M is λDNA digested with HindIII which is employed as molecular size marker). DNA obtained from each colonies was isolated and nucleotide sequence of PIP cDNA insert was determined by dideoxy chain termination method employing Sequenase(United States Biochemical, U.S.A.) and primers such as SK promoter primer and T7 promoter primer. Plasmid thus sequenced was named pJMC511, and deposited with the Korean Culture Center of Microorganisims(KCCM) on Aug. 28, 1993 as deposition No. KCCM 10041.

Meanwhile, as disclosed in FIG. 2, PIP cDNA is consist of 918 bp of one open reading frame and termination codon; and polyadenylation signal which is ubiquitous in mRNA of most plants and animals, appears to be located in the upstream of 33 bp from the polyadenylation site. In FIG. 2, (*) is termination code, and amino acid sequence was written out in accordance with IUPAC nomenclature system.

From the study on nucleotide sequence homology of said PIP genome and PAP genome isolated from cDNA library of Phytolacca americana L., nucleotide sequence homology of about 82% was determined; and, it was also confirmed that PIP cDNA insert codes 305 amino acid residues and 22 residues of which function as signal peptide analogously in the case of PAP. Compared with amino acid sequence of PAP genome, high level of homology of about 81% was determined; and amino acid sequence for active site of PIP and PAP was appeared to be completely same.

As disclosed in FIG. 3, amino acid sequences prevalent in ribosome-inactivating proteins(RIPs: PAP, Abrin A chain, Luffin-a, MAP, Ricin A chain, Trichosanthin and S06) are also found in PIP genome(Ile-Gln-Met-Val-Ser-Glu-Ala-Arg-Phe-Lys-Tyr-Ile), which is assumed to be the active site of RIPs.

EXAMPLE 2

Preparation of expression vector pMS12

For the expression of PIP genome in E. coli HB101, commercially available FLAG™ vector(International Biotechnologies Inc., U.S.A.) was employed. Primers such as 5'-CCAAGCTTGTGAATACCATCATCTA C-3' and 5'-GGAAGCTTAAACTAATCACCAAGATT-3' synthesized by DNA Synthesizer(Applied Biosystems Inc., U.S.A.), were employed as N-terminal primer and C-terminal primer, respectively; and PIP genome was amplified by polymerase chain reaction using Vent™ DNA polymerase(New England Biolab., U.S.A.). In this connection, denaturation(95° C., 30 sec), annealing(55° C., 30 sec) and extension(72° C., 30 sec) were carried out for 30 cycles by DNA Thermal Cycler (Cetus/Perkin-Elmer, U.S.A.). PIP genome thus amplified was cleaved with HindIII, and expression vector of the invention was prepared by ligating HindIII-cleaved PIP gene into HindIII-cleaved FLAG™ vector with T₄ DNA ligase. Expression vector thus prepared was named pMS12; and deposited with the Korean Culture Center of Microorganisims(KCCM) on Aug. 28, 1993 as deposition No. KCCM 10040. The process for stepwise constructing pMS12 is illustrated in FIG. 4. In FIG. 4, `MCS` is employed to mean multicloning site.

pMS12 thus constructed was transformed into competent E. coli HB101 prepared by the treatment of CaCl₂ solution; and, transformant harboring pMS12 was selected from the colonies cultured on LB media containing 50 μg/ml ampicilin, based on plasmid DNA isolation technique employing alkaline lysis method see: Maniatis et al., Molecular Cloning, 368-369(1982)!. FIG. 5 is a photograph showing 0.8% agarose gel electrophoresis pattern of pMS12 digested with HindIII. In FIG. 5, M is molecular size marker, i.e., λDNA cleaved with HindIII, and pMS12 lane shows expression vector pMS12 of the present invention.

EXAMPLE 3

Growth inhibition of microorganism transformed with pMS12

Expression of PAP and MAP genome has been reported to inhibit growth of host microorganism transformed therewith. On the other hand, genome of Ricin which is a kind of RIP, has been reported not to inhibit growth of its transformant. Under the circumstance, whether recombinant PIP inhibits growth of transformant or not, was studied through the investigation of cell growth pattern. Non-transformed E. coli HB101 and transformed E. coli HB101 harboring pFLAG or pMS12 were inoculated on LB media containing 50 μg/ml ampicilin, and incubated overnight. Cultures of the same cell concentration thus incubated were inoculated on LB liquid media containing 0.7 mM IPTG(isopropyl-β-D-thiogalactoside), cultured on shaking incubator at 37° C.; and, cell concentrations were measured as absorbance at 600 nm. As clearly disclosed in FIG. 6, the growth of HB101 harboring pMJ12(o-o) which produce recombinant PAP(KCCM 10037) and HB101(*-*) harboring pMS12 which produce recombinant PIP was inhibited remarkably, while that of non-transformed HB101(Δ-Δ) and transformed HB101(□-□) harboring pFLAG was normal. Accordingly, it was dearly determined that recombinant PIP inhibits the growth of E. coli HB101 transformed with pMS12, analogously in the case of PAP.

EXAMPLE 4

Isolation of recombinant PIP from E. coli HB101 transformed with vector pMS12

E. coli HB101 harboring pMS12 was cultured on 50 ml of LB medium containing 50 μg/ml ampicilin; and recombinant PIP was induced by the addition of 0.75 mM of IPTG when OD₆₀₀ was reached to 1.0. After PIP induction, cells thus cultured were harvested by centrifugation, washed 2 times with phosphate buffered saline(PBS: 0.01M NaH₂ PO₄. 0.15M NaCl, pH 7.4); and, subjected to freezing in dry ice-methanol bath and thawing at 37° C. Then, cell thus treated was emulsified with said buffer solution(pH 8.4) containing 0.25 mg/ml lysozyme; and freezing in dry ice-methanol bath and thawing process was repeated 3 times. Said solution was shaked at an interval of 10 min, kept in 37° C. for 30 min and centrifuged at 25,000×g for 45 min at 4° C. 10 μl of supernatant thus obtained was analyzed by 10% SDS-PAGE, stained with Coomassie brilliant blue R, and destained with destaining solution; and production of recombinant PIP was determined.

To the said supernatant was added 1M CaCl₂ solution, to the final concentration of 1.0 mM and said solution was loaded on anti-FLAG M1 affinity gel column, after washing with 5 ml of glycine-HCl(pH 3.0) and PBS solution 3 times, and with 12 ml PBS/Ca solution(PBS solution containing 1.0 mM CaCl₂) 3 times. 500 μl of PBS/EDTA solution(PBS solution containing 2.0 mM EDTA) was kept for 30 min in the column to which recombinant PIP was bound; and eluted with 500 μl PBS/EDTA solution(PBS solution containing 2.0 mM EDTA) at an interval of 10 min. Amount and purity of recombinent PIP thus isolated were determined by absorbance measurement and SDS-PAGE analysis, respectively. FIG. 7 is a photograph showing SDS-PAGE pattern of purified recombinant PIP(lane 2) and recombinant PAP(lane 3).

EXAMPLE 5

Activity determination of recombinant PIP

For the activity determination of the purified recombinant PIP which inhibits protein synthesis, in vitro translation employing rabbit reticulocyte lysis system(Promega, U.S.A.) was carried out. Recombinant PIP purified in accordance with the Example 4 and dialysed against deionized water by Spectra/Por 2 membrane(Spectrum, U.S.A.) system, was employed to compare with the activity of recombinant PAP.

The reaction mixtures for in vitro translation were disclosed in Table 1.

                  TABLE 1                                                          ______________________________________                                         Reaction mixtures for in vitro translation                                     experi-                                                                        mental                                                                         group control      PIP          PAP                                            ______________________________________                                         reaction                                                                             35 μl rabbit                                                                             35 μl rabbit                                                                             35 μl rabbit                                mixture                                                                              reticulocyte lysate                                                                         reticulocyte lysate                                                                         reticulocyte lysate                                  1 μl .sup.35 S-methionine                                                                1 μl .sup.35 S-methionine                                                                1 μl .sup.35 S-methionine                         (10 mCi/ml)  (10 mCi/ml)  (10 mCi/ml)                                          1 μl RNasin                                                                              1 μl RNasin                                                                              1 μl RNasin                                       (40 U/μl) (40 U/μl) (40 U/μl)                                         2 μl luciferase RNA                                                                      2 μl luciferase RNA                                                                      2 μl luciferase RNA                               (0.5 μg/μl)                                                                           (0.5 μg/μl)                                                                           (0.5 μg/μl)                                    11 μl     11 μl recombinant                                                                        11 μl recombinant                                 Water        PIP (80 pmol)                                                                               PAP (80 pmol)                                  ______________________________________                                    

Each experimental group was incubated at 37° C. for 90 min. Proteins thus synthesized were fractionated by 15% SDS-PAGE, dried with gel dryer and determined by radioautography. FIG. 8 is a photograph showing the results of SDS-PAGE after in vitro translation experiment. As clearly illustrated in FIG. 8, protein synthesis of luciferase(62 KD) is appeared in control group(lane 1), while recombinant PIP(lane 3) and recombinent PAP(lane 2) do not show any protein synthesis.

As clearly illustrated and demonstrated as aboves, the present invention provides a novel genome of PIP isolated from Phytolacca insularis Nakai, which is a kind of ribosome inactivating proteins, and a recombinant expression vector producing said PIP.

    __________________________________________________________________________     SEQUENCE LISTING                                                               (1) GENERAL INFORMATION:                                                       (iii) NUMBER OF SEQUENCES: 2                                                   (2) INFORMATION FOR SEQ ID NO:1:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 918 base pairs                                                     (B) TYPE: nucleic acid                                                         (C) STRANDEDNESS: single                                                       (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: cDNA to mRNA                                               (iii) HYPOTHETICAL: NO                                                         (iv) ANTI-SENSE: NO                                                            (vi) ORIGINAL SOURCE:                                                          (A) ORGANISM: Phytolacca insularis                                             (vii) IMMEDIATE SOURCE:                                                        (B) CLONE: antiviral protein (PIP)                                             (xi) SEQUENCE DESCRIPTION: SEQ ID NO:1:                                        ATGAAGTTGATGCTTGTGGTGACAATATCAGTATGGCTCATTCTTGCACCAACATCTACT60                 TGGGCCGTGAATACCATCATCTACCATGTTGGAAGTACCACCATTAGAAACTATGCAACT120                TTTGGATACTTCGTACTGAAGGCGAAGATCCAAGTTATGTGCTATGGAATACCAATGCTG180                CCCAATATTGGATCAAATCCAAAATACATATTGGTTGAGCTCCAAGGTTCAAATGAAGAA240                GGCATCACACTAATGCTAAGACGAAACAATTTATATGTGATGGGCTATTCTGATCCCTAC300                AACAATAGGTGTCGTTTCCATCTCTTTAAGGCTATCTCAGGTACTGAACGCGAAGATGTA360                GAGACTACTCTTTGCCCAAATGCCGATTCTCGTGTTGGTAAAAACATAAACTATGATAGT420                CGATATCCAACATTGGAATCAAAAGCAGGAGTAAATTCAAGAAGTCGAGTCCAACTGGGA480                ATTCGAATACTCGACAGTGGCATTGGAAGGATTTCTGGAGTGACGTCATTCACTGAGAGA540                ACCGAAGCTGAATTCCTACTGGTAGCCATACAAATGGTATCAGAGGCAGCAAGATTCAAG600                TACATAGAGGATCAAGTGAAAACTAATTTTAACAGACCATTCAACCCTAATCCCAAAGTA660                CTTATATTGCAGGAGACATGGGGTAAGATTTCTTCAGCAATTCATGGTGCCAGGAATGGA720                GTTTTACCCAATCCTCTACAGCTAGTGCATGCCAATGGTGCAAATTGGATAGTGTTGAGA780                GTGGATGAAATCAAGCCTGATGTGTCACTCTTAAACTACGTTATTGGGAGCTGCCAGAGA840                ACTTATAACCAAAATGCCATGTTTTCTCAACTTATAATGTCTACTTATTATAATTACATG900                GCTAATCTTGGTGATTAG918                                                          (2) INFORMATION FOR SEQ ID NO:2:                                               (i) SEQUENCE CHARACTERISTICS:                                                  (A) LENGTH: 305 amino acids                                                    (B) TYPE: amino acid                                                           (D) TOPOLOGY: linear                                                           (ii) MOLECULE TYPE: protein                                                    (iii) HYPOTHETICAL: NO                                                         (v) FRAGMENT TYPE: N-terminal                                                  (vi) ORIGINAL SOURCE:                                                          (A) ORGANISM: Phytolacca insularis                                             (vii) IMMEDIATE SOURCE:                                                        (B) CLONE: antiviral protein (PIP)                                             (xi) SEQUENCE DESCRIPTION: SEQ ID NO:2:                                        MetLysLeuMetLeuValValThrIleSerValTrpLeuIleLeuAla                               151015                                                                         ProThrSerThrTrpAlaValAsnThrIleIleTyrHisValGlySer                               202530                                                                         ThrThrIleArgAsnTyrAlaThrPheGlyTyrPheValLeuLysAla                               354045                                                                         LysIleGlnValMetCysTyrGlyIleProMetLeuProAsnIleGly                               505560                                                                         SerAsnProLysTyrIleLeuValGluLeuGlnGlySerAsnGluGlu                               65707580                                                                       GlyIleThrLeuMetLeuArgArgAsnAsnLeuTyrValMetGlyTyr                               859095                                                                         SerAspProTyrAsnAsnArgCysArgPheHisLeuPheLysAlaIle                               100105110                                                                      SerGlyThrGluArgGluAspValGluThrThrLeuCysProAsnAla                               115120125                                                                      AspSerArgValGlyLysAsnIleAsnTyrAspSerArgTyrProThr                               130135140                                                                      LeuGluSerLysAlaGlyValAsnSerArgSerArgValGlnLeuGly                               145150155160                                                                   IleArgIleLeuAspSerGlyIleGlyArgIleSerGlyValThrSer                               165170175                                                                      PheThrGluArgThrGluAlaGluPheLeuLeuValAlaIleGlnMet                               180185190                                                                      ValSerGluAlaAlaArgPheLysTyrIleGluAspGlnValLysThr                               195200205                                                                      AsnPheAsnArgProPheAsnProAsnProLysValLeuIleLeuGln                               210215220                                                                      GluThrTrpGlyLysIleSerSerAlaIleHisGlyAlaArgAsnGly                               225230235240                                                                   ValLeuProAsnProLeuGlnLeuValHisAlaAsnGlyAlaAsnTrp                               245250255                                                                      IleValLeuArgValAspGluIleLysProAspValSerLeuLeuAsn                               260265270                                                                      TyrValIleGlySerCysGlnArgThrTyrAsnGlnAsnAlaMetPhe                               275280285                                                                      SerGlnLeuIleMetSerThrTyrTyrAsnTyrMetAlaAsnLeuGly                               290295300                                                                      Asp                                                                            305                                                                            __________________________________________________________________________ 

What is claimed is:
 1. Phytolacca antiviral protein isolated from Phytolacca insularis Nakai comprising the amino acid sequence: ##STR1##
 2. Phytolacca insularis antiviral protein produced by the process comprising the step of culturing E. coli HB101 transformed with the expression vector pMS12 (Accession No. KCCM 10040). 